from Wiktionary, Creative Commons Attribution/Share-Alike License

adj. Pertaining to or affected by noxious vapours; dejected, stupified.

n. Moisture; humidity; dampness.

n. Fog; fogginess; vapor.

n. Dejection or depression.

n. A gaseous product, formed in coal mines, old wells, pits, etc.

v. To dampen; to render damp; to moisten; to make humid, or moderately wet; as, to damp cloth.

v. To put out, as fire; to depress or deject; to deaden; to cloud; to check or restrain, as action or vigor; to make dull; to weaken; to discourage.

v. To suppress vibrations (mechanical) or oscillations (electrical) by converting energy to heat (or some other form of energy).

from the GNU version of the Collaborative International Dictionary of English

adj. Being in a state between dry and wet; moderately wet; moist; humid.

adj. Dejected; depressed; sunk.

n. Moisture; humidity; fog; fogginess; vapor.

n. Dejection; depression; cloud of the mind.

n. A gaseous product, formed in coal mines, old wells, pints, etc.

intransitive v. To render damp; to moisten; to make humid, or moderately wet; to dampen.

intransitive v. To put out, as fire; to depress or deject; to deaden; to cloud; to check or restrain, as action or vigor; to make dull; to weaken; to discourage.

from The Century Dictionary and Cyclopedia

Moist; humid; moderately wet: as, a damp cloth; damp air.

Clammy.

Dejected; depressed.

Synonyms Humid, Dank, etc. See moist.

To moisten; make humid or moderately wet; dampen.

To extinguish; smother; suffocate.

To suffocate with damp or foul air in a mine. [Eng.]

To check or retard the force or action of: as, to damp a fire by covering it with ashes; especially, to diminish the range or amplitude of vibrations in, as a piano-string, by causing a resistance to the motions of the vibrating body.

To make dull or weak and indistinct, as a sound or a light; obscure; deaden.

To depress; deject; discourage; deaden; check; weaken.

Specifically To diminish or destroy the oscillation of (a metallic body in motion in a magnetic field).

[Dampen is now more common in the literal sense, and is sometimes used in the derived senses.]

Synonyms To moderate, allay, dispirit.

In horticulture, to rot or waste away, as the stems and leaves of seedlings and other tender plants, when the soil and atmosphere in which they are vegetating are too wet or cold: with off: as, flower-seedlings in hotbeds are especially liable to damp off.

n. Moist air; humidity; moisture.

n. A poisonous vapor; specifically, in mining, a stifling or poisonous gas. See black-damp, fire-damp.

n. A fog.

n. A check; a discouragement.

n. Depression of spirits; dejection.

n. The popular name of a disease which attacks young seedlings and succulent plants, causing them to rot off near the surface of the ground.

It also means crouching in damp sand at playgrounds and wiping snotty noses and shitty bums and worrying constantly about whether or not you remembered to restock the diaper bag and, also, refill your Ativan prescription.